全文获取类型
收费全文 | 1356篇 |
免费 | 60篇 |
国内免费 | 1篇 |
出版年
2023年 | 9篇 |
2021年 | 18篇 |
2020年 | 20篇 |
2019年 | 14篇 |
2018年 | 49篇 |
2017年 | 32篇 |
2016年 | 55篇 |
2015年 | 36篇 |
2014年 | 71篇 |
2013年 | 95篇 |
2012年 | 55篇 |
2011年 | 46篇 |
2010年 | 56篇 |
2009年 | 38篇 |
2008年 | 37篇 |
2007年 | 25篇 |
2006年 | 39篇 |
2005年 | 24篇 |
2004年 | 19篇 |
2003年 | 20篇 |
2002年 | 26篇 |
2001年 | 19篇 |
2000年 | 26篇 |
1999年 | 19篇 |
1998年 | 24篇 |
1997年 | 15篇 |
1996年 | 18篇 |
1995年 | 12篇 |
1994年 | 20篇 |
1993年 | 13篇 |
1992年 | 13篇 |
1991年 | 21篇 |
1988年 | 9篇 |
1987年 | 16篇 |
1985年 | 17篇 |
1984年 | 10篇 |
1983年 | 9篇 |
1982年 | 18篇 |
1981年 | 24篇 |
1980年 | 19篇 |
1979年 | 16篇 |
1978年 | 13篇 |
1977年 | 19篇 |
1976年 | 20篇 |
1975年 | 17篇 |
1974年 | 17篇 |
1973年 | 9篇 |
1972年 | 13篇 |
1969年 | 10篇 |
1960年 | 8篇 |
排序方式: 共有1417条查询结果,搜索用时 15 毫秒
1.
2.
A systematic study of transformation reactions of Actinomycetes with respect to the progesterone molecule was undertaken. The results obtained, i.e. the types of transformation reactions in different actinomycete species, were evaluated from the point of view of taxonomy. The actinomycetes tested were divided according to the transformation types into three groups: (1) a group of species transforming progesterone in the 16α-position; (2) a group of species transforming progesterone in the β-position; (3) a group of species in which no capacity to transform progesterone into another steroid derivative was established. From the point of view of Actinomycete classification the transformation reactions on the steroid molecule fulfil all the requirements of taxonomic features of Actinomycetes. They appear to be specific properties, independent of strictly cultivation conditions and common to all the strains of individual actinomycete species tested. 相似文献
3.
Dr. Lad Čelakovský 《Plant Systematics and Evolution》1890,40(8):287-297
Ohne Zusammenfassung 相似文献
4.
Aileen F. G. Bongat Rina Saksena Roberto Adamo Yukari Fujimoto Zenyu Shiokawa Dwight C. Peterson Koichi Fukase Willie F. Vann Pavol Kováč 《Glycoconjugate journal》2010,27(1):69-77
Using recombinant tetanus toxin HC fragment (rTT-HC) as carrier, we prepared multimeric bivalent immunogens featuring the synthetic hexasaccharide fragment of O-PS of Vibrio cholerae O:1, serotype Ogawa, in combination with either the synthetic hexasaccharide fragment of O-PS of Vibrio cholerae O:1, serotype Inaba, or a synthetic disaccharide tetrapeptide peptidoglycan fragment as adjuvant. The conjugation reaction
was effected by squaric acid chemistry and monitored in virtually real time by SELDI-TOF MS. In this way, we could prepare
well-defined immunogens with predictable carbohydrate–carrier ratio, whose molecular mass and the amount of each saccharide attached could be independently determined. The ability to prepare such neoglycoconjugates opens unprecedented possibilities
for preparation of conjugate vaccines for bacterial diseases from synthetic carbohydrates. 相似文献
5.
Dr. Lad Čelakovský 《Plant Systematics and Evolution》1872,22(9):283-285
Ohne Zusammenfassung 相似文献
6.
Summary A support based on pyrogeneous silicon dioxide of particle size 0.01 to 0.1/um, modified by 3-(amino)propyltriethoxysilane and activated by glutaraldehyde was employed for the immobilization of concanavalin A, immunoglobulins, basic pancreatic trypsin inhibitor, and chymotrypsin. Its binding capacity is comparable with that of porous supports while the biological activity of the proteins immobilized is retained. Nonspecific adsorption of these proteins to the support is low compared to its binding capacity. 相似文献
7.
Twelve metronidazole-resistant and twelve metronidazole-susceptible strains ofTrichomonas vaginalis were tested for the presence of dsRNA. Three resistant and five susceptible strains were found to contain dsRNA which indicated
that metronidazole resistance does not correlate with the absence of dsRNA. Electron microscopy showed the homogenates of
all dsRNA -positive strains to contain virus-like particles 32 –38 nm in diameter, while no such particles were found in the
dsRNA-negative strains. A mutual relationship between the dsRNA and virus-like particles seems to exist.
After this paper had been accepted for publication the occurrence of virus-like particles in dsRNA-positive trichomonads was
reported by others (Wang A.L., Wang C.C.: The double stranded RNA inTrichomonas vaginalis may originate from virus-like particles.Proc. Nat. Acad. Sci. USA
83, 7956–7961, 1986). 相似文献
8.
J. Čatský D. K. Velichkov Jana Pospísilová Jarmila Solárová Ingrid Tichá 《Biologia Plantarum》1987,29(5):355-364
The carbon balances of whole, 21-d old French bean plants (Phaseolus vulgaris L.) grown in standard nutrient solution (1K) and its modifications without (OK) or surplus (2K) potassium were calculated
from the daily photosynthetic carbon inputs of individual leaves, and the daily respiratory carbon losses by individual leaves,
stalks and petioles, and roots. Under the three K concentrations, maximum net photosynthetic rates (Pn) were found in the 2nd or in the 3rd trifoliate leaves, maximum respiratory rates (Rd) in the youngest, 4th trifoliate leaves; the Pn/Rd ratio decreased with leaf age. In all leaves of 2K plants, leaf dry masses and thicknesses, Pn, Pn/Pd ratios, and stomatal and intracellular conductances were lower than in OK and IK plants. Daily whole-plant net carbon gain
was highest in IK plants, whereas in OK and 2K plants it was 98.0 and 81.3 % of IK, respectively. Similar values were found
in the parameters of growth analysis, namely in net assimilation rates and relative growth rates.
No differences were found in water potential (Ψ
w
) or water saturation deficit (Wsat) in the OK, 1K and 2K plants sufficiently supplied with water or during wilting and resaturation. The decrease in Ψw to −0.97 MPa was associated with a 19.9 %, 31.4 % and 23.4 % decrease in Pn of OK, 1K and 2K plants, respectively, but no effect on Rd was found. In the three variants, the short-time effect of mild water stress was fully reversible. 相似文献
9.
Interactions between intrinsic regulation and neural modulation of acetylcholinesterase in fast and slow skeletal muscles 总被引:2,自引:0,他引:2
Janez Sketelj Neva Črne-Finderle Samo Ribarič Miro Brzin 《Cellular and molecular neurobiology》1991,11(1):35-54
1. Initiation of subsynaptic sarcolemmal specialization and expression of different molecular forms of AChE were studied in fast extensor digitorum longus (EDL) and slow soleus (SOL) muscle of the rat under different experimental conditions in order to understand better the interplay of neural influences with intrinsic regulatory mechanisms of muscle cells. 2. Former junctional sarcolemma still accumulated AChE and continued to differentiate morphologically for at least 3 weeks after early postnatal denervation of EDL and SOL muscles. In noninnervated regenerating muscles, postsynaptic-like sarcolemmal specializations with AChE appeared (a) in the former junctional region, possibly induced by a substance in the former junctional basal lamina, and (b) in circumscribed areas along the whole length of myotubes. Therefore, the muscle cells seem to be able to produce a postsynaptic organization guiding substance, located in the basal lamina. The nerve may enhance the production or accumulation of this substance at the site of the future motor end plate. 3. Significant differences in the patterns of AChE molecular forms in EDL and SOL muscles arise between day 4 and day 10 after birth. The developmental process of downregulation of the asymmetric AChE forms, eliminating them extrajunctionally in the EDL, is less efficient in the SOL. The presence of these AChE forms in the extrajunctional regions of the SOL correlates with the ability to accumulate AChE in myotendinous junctions. The typical distribution of the asymmetric AChE forms in the EDL and SOL is maintained for at least 3 weeks after muscle denervation. 4. Different patterns of AChE molecular forms were observed in noninnervated EDL and SOL muscles regenerating in situ. In innervated regenerates, patterns of AChE molecular forms typical for mature muscles were instituted during the first week after reinnervation. 5. These results are consistent with the hypothesis that intrinsic differences between slow and fast muscle fibers, concerning the response of their AChE regulating mechanism to neural influences, may contribute to different AChE expression in fast and slow muscles, in addition to the influence of different stimulation patterns. 相似文献
10.
Condensation of 2,4,6-tri-O-acetyl-3-deoxy-3-fluoro-α-
-galactopyranosyl bromide (3) with methyl 2,3,4-tri-O-acetyl-β-
-galactopyranoside (4) gave a fully acetylated (1→6)-β-
-galactobiose fluorinated at the 3′-position which was deacetylated to give the title disaccharide. The corresponding trisaccharide was obtained by reaction of 4 with 2,3,4-tri-O-acetyl-6-O-chloroacetyl-α-
-galactopyranosyl bromide (5), dechloroacetylation of the formed methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β-
-galactopyranosyl)-(1→6)- 2,3,4-tri-O-acetyl-β-
-galactopyranoside to give methyl O-(2,3,4-tri-O-acetyl-β-
-galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β-
-galactopyranoside (14), condensation with 3, and deacetylation. Dechloroacetylation of methyl O-(2,3,4-tri-O-acetyl-6-O-chloroacetyl-β-
-galactopyranosyl)-(1→6)-O-(2,3,4-tri-O-acetyl- β-
-galactopyranosyl)-(1→6)-2,3,4-tri-O-acetyl-β-
-galactopyranoside, obtained by condensation of disaccharide 14 with bromide 5, was accompanied by extensive acetyl migration giving a mixture of products. These were deacetylated to give, crystalline for the first time, the methyl β-glycoside of (1→6)-β-
-galactotriose in high yield. The structures of the target compounds were confirmed by 500-MHz, 2D, 1H- and conventional 13C- and 19F-n.m.r. spectroscopy. 相似文献